\documentclass[10pt]{report}
\usepackage[centering,paperwidth=70mm,paperheight=100mm,body={170pt,210pt}]{geometry}

\begin{document}

some text
\footnote{footnote at bottom}

\newpage

\noindent
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more text
\footnote{footnote in the middle.}

\section{A new section}

\end{document}
